Fabricationless semiconductor companies or entities utilize commercial computer aided design (CAD) tools, foundry services, packaging, and final test facilities within other companies and even other countries. Little effort is made today to insure that a design implemented and released for fabrication is the same design as originally created. For a number of reasons, some of which are clandestine, the design can be altered. Governments can be especially sensitive to such a practice regarding homeland defense electronics.
In today's environment where CAD tools, fabrication, packaging and test can all be accomplished in locations or with tools outside the control of a designer, it is possible for “extra” logic to be inserted for clandestine purposes. For example, an outside entity may wish to insert extra logic to monitor or introduce new control modes within a real time processor. Or a foreign government may desire to insert extra logic for strategic military purposes.
Accordingly, it is desirable to create a hardware structure that allows the designer to determine if extra electronics has been inserted into a design.